A known active noise control device involves active noise control as a technique for reducing noise in a target space (noise propagation passage) in which a sound generated from a noise source propagates. The active noise control is a technique for actively reducing noise by outputting a cancelling sound having an antiphase to the phase of the noise and having an amplitude identical with the amplitude of the noise.
Such an active noise control device has a problem that reflection of the sound propagating in the target space degrades the noise cancellation performance of the active noise control device. To solve this problem, it has been proposed to multiply a filter coefficient by a window function so as to suppress degradation in the noise cancellation performance due to a reflection wave (for example, see Patent Literatures 1 to 3).
In the active noise control device, a change of environmental conditions such as the temperature, humidity, and atmospheric pressure in the target space and/or a disturbance component such as an intruding extraneous sound may cause oscillation and/or divergence leading to the degradation in the noise cancellation performance. However, the above-described Patent Literatures 1 to 3 are directed to suppress the degradation in the noise cancellation performance due to the reflection of the sound propagating in the target space, and therefore, it has been difficult to suppress the degradation in the noise cancellation performance due to the disturbance component.